Is it bad if cofounders split a company evenly, but one cofounder provides all the seed capital?

Not exactly sure how you mean skew the split, but here are the issues I see:

If you are both putting in something of major value to the company and those values are somewhat similar, that may be okay to split it as you discuss. It depends upon your business and finance plans to some extent as well, e.g. how much more will be needed in terms of capital and how involved he will be in the business operations.

If he is just supposed to be a passive investor, what are the terms of conversion and when does that occur because when it does and it sounds like he gets 50% equity, how will a voting tie be handled? You need to look to state law and your bylaws or articles of incorporation to see what voting percentages are needed for certain corporate actions to be taken. A lot of M&A and funding (i.e. equity issuances) require certain majority voting of shareholders of the corporation (sometimes simply majority over 50%, sometimes more), so you need to understand how voting percentages can affect you down the road.

If you bring a lot of value and leadership to the company, you should probably try to bring the balance to your favor so you won't lose control of majority voting rights. Also, can you pre-pay the note prior to conversion to buy him out if you bring in further rounds? These can all be issues to consider in answering your question; however, cash is king and sometimes you can't cover all possible future strategic issues, so just getting the money in the door may be the most important thing right now.